AMMONIA (NH3) or its ion form ammonium (NH4+) is an important source of nitrogen for living systems and is ubiquitously present in the nature. Simple, direct and automation-ready procedures for measuring NH3 are very desirable. This ammonia/ammonium assay is based on an improved o-phthalaldehyde Method. This reagent reacts with ammonia/ ammonium and forms a fluorescent product. The fluorescence intensity (lambda ex/em = 360/450nm) is proportional to the ammonia concentration in the sample.